Developing with Web API

Discovery and access

Introduction

The term Web API is generically used for referring to some implementation of an application programming interface for Web applications. As such, a Web API may be a RESTful API or a library implemented in some web application language. The ENERGIC OD VH uses the term Web API in the latter sense, to identify a Javascript library facilitating the development of web and mobile apps using the capabilities of VHs.

The ENERGIC OD Web API is a Javascript library providing a set of predefined software objects whose properties and behaviour hide the complexity of the interaction with the VH, presenting the developer only significant methods.

Figure 9 shows the main Web API’s objects and their behavior in a typical application:

DAB: It is the Web API entry point. This object represents a VH discovery and access broker which is capable to access heterogeneous data sources in a homogeneous way. During the creation phase, it is associated to a specific VH instance. It provides discovery capabilities to find relevant datasets provided by the VH.
ResultSet: An object provided as a result of a DAB discovery operation. It represents a set of datasets matching the DAB discovery constraints.
Paginator: An object associated to the ResultSet which allows to retrieve results as subsets (pages). It helps handling results avoiding long and unmanageable lists.
Page: An object representing a subset of a ResultSet.
GINode: An object representing a geoinformation resource (typically a dataset) which is a single result of the discovery operation and part of a Page.
Layer: An object which is a dataset representation ready to be used by other Javascript libraries and environments like OpenLayers.

The main concepts represented as objects in the Web API

The discover method of the DAB object, allows to retrieve a ResultSet object, containing all the GINode objects satisfying the query contraints which are specified as a JSON object passed to the discovery call. The access to the GINode objects is mediated by a Paginator object linked with the ResultSet, which allows to access limited sets of GINodes as Pages. The GINode content can be accessed as a layer of different types.

The full Web API documentation available online provides a detailed description of objects, properties, and methods including examples and live demos.

The endpoint for the DAB object configuration for accessing the pan-European Virtual Hub is:

http://vh-eu.energic-od.eu/gi-cat/services/opensearch